Information storage devices typically include semiconductor memories such as RAM or electromechanical memories such as hard disk drive systems. Electromechanical memories are sometimes termed mass storage devices, as they are typically more cost effective than semiconductor memories, but may suffer from slower access times and data rates.
Conventional hard disk drive systems employ at least one rotating disk having magnetic media layers adjacent to both its major surfaces. Transducers or heads are typically held adjacent to each major surface for writing and/or reading information on the media layers. An arm holding the transducers is moved by an actuator to position the transducers adjacent to various tracks of the rapidly spinning disk. A "linear actuator" typically moves an arm toward and away from a center of the disk along a radius of the disk with which the arm is aligned, whereas a "rotary actuator" rotates an arm about a pivot at a side of the disk to sweep the suspension and transducer across the disk surface.
For increased storage capacity, several disks are commonly provided in a single information storage system, each disk having an associated pair of heads for transducing information via each major surface of the disk. The suspension arms for each pair of these heads are commonly mounted to an actuator arm, with the actuator arms extending from an "E-block" and the connected heads, suspension arms and E-block forming a "head-stack assembly." A rotary actuator moves the E-shaped block to cause all the suspension arms and heads to sweep across the disks in tandem. In addition to increasing overall storage capacity, multi-disk drives can decrease access time. More significant increases in data rates are afforded by improvements in transducer and drive electronics.
Conventional disk drives have signal amplifiers that are located on the E-block so that the mass and size of the amplifier chips do not interfere with the positioning of the heads on the disks. Signals between the heads and amplifiers have typically been carried by twisted wires which are held in tubing that runs along the sides of the suspension arm. Head-amplifier signals are modernly carried by electrical traces deposited on the suspension arms, or flexible circuit boards attached to the suspension arms, with additional flexible cables extending along the actuator arms to reach the amplifier. Inductance in the conductors between the heads and amplifiers is a bottleneck in high data rate applications, but can be reduced by shortening the length of the conductors, implying moving the amplifiers closer to the heads.
Some inventions have proposed placing an amplifier atop the suspension arm along with the conductors. Unfortunately, this can adversely affect the dynamic performance of the suspension arm, and it may be difficult to make the amplifier thin enough to avoid contact with the disk during operation. Other inventions propose inserting a signal booster element such as a transformer into the conductors that run along the flexures, held by the tubing. Proposals also exist to locate a preamplifier chip on each suspension arm, connected to conductive traces that run on the disk-facing side of each suspension arm. A difficulty with this approach is that the preamplifier chips are each exposed adjacent to a disk and during actuation sweep across the disk surface, which becomes more problematic in the event of a shock to the drive. This limits the size of the chips or, conversely, the size of the chips limits the spacing between disks. Many of these approaches are also constrained by manufacturing difficulties.